In the existing Global System for Mobile Communications (referred to as GSM) system, A interface is adopted to communicate between a Mobile Switching Center Server (referred to as MSC Server) and a Base Station Controller (referred to as BSC), while a Mobile Terminal (referred to as MS) communicates with a Base Transceiver Station (referred to as BTS) via an air interface of Um interface. In addition, the BTS is connected with BCS via an Abis interface. Additionally, a Base Station Subsystem (referred to as BSS) composed of the BSC and BTS, as well as the MSC and MGW are all one part of a Core Network (referred to as CN).
At present, in a calling and called process of the GSM system, a user-plane speech of a caller party is transferred to a Media Gateway (referred to as MGW) via the BSS, and then is transferred to the BSS of an opposite party by the MGW, even if the two parties of a call are in the same BSS. However, there are a large number of local calls in an actual GSM network, that is the two parties of the call are in the same BSS, or belong to the different BTSs of the same BTS cluster, or belong to the same BSC. For the local calls, the following questions will appear if the current call handling process is followed.
For calls belonging to the same BTS, the case that a user-plane speech of a caller party is transferred to the BSC via the Abis interface of the BTS, the BSC transfers the user-plane speech to the MGW via the A interface, the MGW transfers the user-plane speech to the original BSC via the A interface, and then the original BSC transfers the user-plane speech to the original BTS will occur, thus resulting in the loss of transmission resources between the Abis interface and the A interface.
For calls belonging to the different BTSs of the same BTS cluster, the case that a user-plane speech of a caller party is transferred to the BTS controlled by the BTS cluster via the Abis interface of the BTS, the controlled BTS transfers the user-plane speech to the BSC via Abis interface of the BTS, the BSC transfers the user-plane speech to the MGW via the A interface, the MGW transfers the user-plane speech to the original BSC via the A interface, the original BSC transfers the user-plane speech to the above controlled BTS, and then the above controlled BTS transfers the user-plane speech to the original BTS will occur, thus resulting in the loss of transmission resources of the Abis interface between the above controlled BTS and the BSC, as well as the loss of transmission resources of the A interface.
As shown in FIG. 1, for calls belonging to the same BSC, the case that the BSC transfers a user-plane speech to the MGW via the A interface at first, and then the MGW transfers the user-plane speech to the BSC via the A interface will occur, thus resulting in the loss of transmission resources of the A interface.
In order to avoid the loss of the type of the transmission resources, a local switch function is provided. The local switch function refers to a function for switching voice data of two parties through BSS, and the switch of the user-plane speech of the two parties is performed by the BSS for the two parties of the call under the same BSS, just as shown in FIG. 2.
However, if one party of the call needs to perform the handover after using the local switch, such as needing to perform the handover from the original BSC to another BSC, the two parties of the call are no longer provided with services by the same BSC, therefore the local switch function will no longer continue to be used.
When a call using the local switch function needs to perform the handover, the method adopted by the existing scheme is to stop using the local switch at first, to restore the mode for switching through the core network, and then to perform the handover in accordance with the existing handover process, as shown in FIG. 3. However, the method requires releasing the local switch at first, and then executes the handover, thus delaying the handover time. At the same time, the local switch is also required to be established again if the handover fails.